Oh, that’s super clever integration with tracing. Feel free to send us a PR; we’ll link to this as a related project in the docs!
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Due to reliance on core_intrinsics it is necessary to develop using nightly Rust, but there are stubs in place so a production build will not require nightly.
I recently released version 0.2 which includes no_std support and adds optional log message arguments to the ensure macro.